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automatic furnace won't light

My furnace is a tempstar furnace it does have a blinking light which is saying everything is normal but when it's on it won't light so it's jus blowing cold air HELP


  • aircooled81
    aircooled81 Member Posts: 205
    Please be careful, not sure of your limitations here. Too many posibilities to choose based on your vague description BTW.
    If you smell gas, shut it down and call someone. Flame roll out can be dangerous, and dont be taking things apart and testing unless you are confident/compident in doing so.
    Read the instructions, most manufactures instalation and operating instructions can be found on-line.
    Last reminder, electricity can kill, gas can kill, be careful.

    Can you describe the stages it goes through toward ignition? Or atleast what you observe or here when you set the stat to heat?

    Could be something simple like someone shut off the gas valve, or the filter is plugged/dirty and the furnace does come on briefly before tripping on high limit from lack-of-airflow.

    Typically a call for heat at the thermostat, then:
    If theres an induced draft motor, this will come on and likely need to be proven by either end switch on motor or pressure sensor that compares flue box to atmosphere;
    Pilot will need to be proved, through ignition of pilot to flame in contact with sensor, or if you have a hot surface ignitor this will need to glow (2 ways I can see operation, you can advise if you have HSI);
    Then once pilot flame is proven, main burners will light.

    Providing no safeties have open, such as flame roll-out switch, high temp limit switch in flue or furnace, no proof of pilot, no proof of induced draft motor.

  • Tim McElwain
    Tim McElwain Member Posts: 4,608
    The fact that it is blowing cold air says that one or more limits on the furnace are open when they should be closed. Check pressure switch, high limit, blocked vent switch, flame rollout switch (there could be two) and auxillary limit (usually in the blower compartment depending on unit).
  • neilc
    neilc Member Posts: 2,667
    R U cycling the power or service disconnect off and on ?
    my carrier will purge the heating fan for about a minute when power is restored, then the normal burner prepurge, before finally firing.
    R U waiting long enough ?
    R we even talking about a direct vent,
    or a atmospheric ?

    time to call service guy.
    known to beat dead horses